1. Field of the Invention
The present invention relates to telecommunication networks and, more particularly, to a method and system for routing calls directed to non-geographic wireless directory numbers in a telecommunications network.
2. Background of the Art
In known telecommunications networks, a wireline telephone number or directory number (DN) is associated with a fixed geographic location and is served by a single wireline switch. In a wireless network, however, a wireless DN is associated with multiple geographic locations and is served by any one of a number of wireless switches depending on the specific geographic location of the associated mobile wireless device (hereinafter mobile wireless station or wireless station) at the time a call is made. This portability of a wireless DN is one of the basic attributes of wireless telephony, and is often referred to as “roaming”.
In the present implementation of wireless networks, each mobile directory number is associated by both the wireless and wireline networks with a specific geographic home switch location. The home switch location includes a physical connectivity matrix and a stored program control section that houses the logic and algorithms necessary to control the connectivity. Associated with wireless switches is a collection of Radio Frequency (RF) channels, aggregated in multiple physical locations called cell sites across a specific area corresponding to a serving market, and variously known in the United States under the designations MSA, RSA, MTA, and BTA, depending on the FCC license.
A pair of entities known as a home location register (HLR) and visitor location register (VLR) in a telecommunications network provide seamless roaming or call delivery when a call is placed to or from a wireless DN. A home location register is associated with a home wireless switch where a wireless DN resides (i.e., the wireless switch to which all incoming wireline-originated calls to the wireless DN are directed). A mobile wireless station is located within its home area when the wireless station can directly communicate with its associated home wireless switch (i.e., located in the area covered by the home wireless switch).
A visitor location register is associated with a wireless switch currently serving a wireless station that is outside of its home area. A wireless station is outside of its home area (or roams) when the wireless station cannot directly communicate with the home wireless switch, and instead communicates with another wireless switch, which is referred to as a visited wireless switch.
Typically, when the VLR and HLR are physically in the same location, the mobile wireless station is “Home” and is not roaming. When the VLR and the HLR are not in the same location and specialized protocols are not implemented to make the wireless station act as if it were “Home”, then the wireless station is “roaming”.
Phone calls from a land-based terminal or station to a mobile wireless station can be completed while roaming only by a carefully orchestrated set of interactions between the HLR and VLR, all of which are described and defined by ANSI-41. ANSI-41 defines the HLR as a logically and possibly physically separate device from the actual switching matrix underlying the RF portion of the wireless network for the home location for the mobile wireless station. Similarly, the VLR is defined as a logically and possibly physically separate device from the actual switching matrix underlying the RF portion of the wireless network from which a mobile wireless station is currently being served. This physical separation, together with the Signaling System Seven (SS7) and the associate messages and protocols, are existing underlying components utilized by the invention.
One problem with known telecommunication networks is that two connections must be established when a call is placed to a wireless DN whose associated wireless station is outside of its home area. In such instances, the telecommunications network first establishes a connection to the home wireless switch associated with the wireless DN. That is, in the existing art, the wireline station call is first routed from the serving wireline switch to the home wireless switch (the HLR location), possibly by way of additional local or Inter-Exchange Carrier (IXC) switches. The home wireless switch then establishes a second connection to a visited wireless switch that currently serves the wireless DN. In particular, the HLR interacts with the VLR to obtain a Temporary Local Directory Number (TLDN) from the allocations made for the physical location of the visited wireless switch serving the wireless station. The wireless switch containing the HLR routes the call via the public switched telephone network (PSTN) to the wireless switch containing the VLR, which then establishes the necessary wireless RF connection to the mobile wireless station. Thus, two separate PSTN connections must be made to complete a single land-to-mobile call while roaming.
As an illustration, FIG. 1 shows a block diagram of a conventional telecommunications network 100. Telecommunications network 100 comprises a wireline switch 110, a home wireless switch 120, a home location register 130, a signal transfer point (STP) 135, a visitor location register 140, a visited wireless switch 150, a wireline telephone 155, a cell site including antenna 170, and a wireless station 175.
Typically, a wireline subscriber using telephone 155 initiates a call request 180a, by dialing the wireless DN associated with wireless station 175. When wireline switch 110 receives call request 180a, wireline switch 110 establishes a first connection 180b via a Public Switched Telephone Network PSTN)160 to home wireless switch 120, which is the home switch associated with the dialed DN.
Home wireless switch 120 sends an ANSI-41 RouteRequest message 180c to its associated home location register 130, requesting the current location of wireless station 175. The text of “Interim Standard (IS) 41”, Revision D, has been adopted to become the ANSI-41 standard. The IS-41, Rev. D, standard is described in “Radio Telecommunications Intersystem Operations,” ANSI/TIA/EIA/41-D-1997, which is incorporated herein by reference. The ANSI-41 Standard describes the communication protocol between home wireless switch 120, home location register 130, visitor location register 140, and visited wireless switch 150 in telecommunications network 100. It should be understood that although the ANSI-41 standard is referred to herein, the features and capabilities of IS-41 Revision A have been found sufficient to enable the present invention.
If wireless station 175 is outside of its home area, as shown in FIG. 1, home location register 130 then identifies the visitor location register with which wireless station 175 was last registered, for example, visitor location register 140, and sends an ANSI-41 RouteRequest message 180d via STP 135 to visitor location register 140.
Visitor location register 140 forwards RouteRequest message 180d to its associated visited wireless switch 150, requesting a route to wireless station 175. Visited wireless switch 150 computes a temporary local directory number (TLDN), which can be used in establishing incoming calls to wireless station 175. Visited wireless switch 150 then returns the TLDN to visitor location register 140 in an ANSI-41 message 180e. Visitor location register 140 then sends, via STP 135, to home location register 130, an ANSI-41 RouteRequest response message 180f that includes the TLDN.
Home location register 130 forwards RouteRequest response message 180f to home wireless switch 120. Using the TLDN in RouteRequest response message 180f, home wireless switch 130 then establishes a second connection 180g to visited wireless switch 150, which sends a ring signal to wireless station 175. Thus, to establish a call between telephone 155 and wireless station 175 when wireless station 175 is outside of its home area, telecommunications network 100 must establish two separate connections 180b and 180g. 
Another problem with conventional methods of routing land-to-mobile calls is that they are dependent on a known geographic “home” for the wireless DN in the home wireless switch. That is, certain directory numbers cannot be used as wireless DN's using the conventional approach shown in FIG. 1. These directory numbers include non-geographic numbers (e.g., NANP directory numbers to which no geographic territory has been assigned) and/or non-dialable numbers (e.g., directory numbers not provided for under the NANP). This unavailability is because such numbers are not routable under conventional approaches, inasmuch as they have no geographic endpoint (i.e., there is no “home ” wireless switch for a non-geographic directory numbers). This unavailability reduces the capacity of the telecommunications network, as well as its efficiency.
In addition, another problem arises with conventional methods of routing land-to-mobile calls. With conventional methods, a wireless mobile station is assigned to a single home area. Accordingly, land-to-mobile calls that are originated outside of the home area are long distance calls. These long distance calls are subject to higher billing rates, which may discourage potential callers from dialing the wireless mobile station. In a scenario in which these potential callers are business associates or clients who are located in regions outside of the subscriber's home area, the higher billing rates may undesirably inhibit growth of the subscriber's client base or may result in a loss of some business associates or clients because the business associates or clients do not wish to place long distance calls.
Accordingly, there is a need for a method and system for establishing land-to-mobile calls that minimizes or eliminates one or more problems as set forth above.